Magnesium alloy member

ABSTRACT

There is provided a magnesium alloy member that includes an aluminum-containing magnesium alloy material. The magnesium alloy material has a modified layer formed at a surface thereof in such a manner that at least a surface of the modified layer has a higher aluminum content than that of any unmodified base portion of the magnesium alloy material.

BACKGROUND OF THE INVENTION

The present invention relates to a surface modification technique for amagnesium alloy material and, more particularly, to a magnesium alloymember consisting of or comprising a magnesium alloy material formedwith a surface modified layer to achieve good adhesion (bonding/coating)properties.

In recent years, there are increasing applications of not only resinmaterials such as polyethylene resins and polypropylene resins but alsolight metal materials such as aluminum alloys and magnesium alloys forvehicle weight reductions. Various surface modification techniques,bonding techniques and coating techniques have been developed to producecomposites of light metal materials or composites of light metalmaterials and other materials. One of the surface modificationtechniques is surface treatment of a metal material with a chromium-freeacidic composition. For example, Patent Document 1 discloses a surfacemodification technique that forms a coating film on a metal material bysurface treatment with an aqueous corrosion-resistant coating solution,and then, fixes the coating film to the metal surface by baking anddrying without water washing.

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    5-195244

SUMMARY OF THE INVENTION

The surface modification technique of Patent Document 1 does not involvea chemical reaction to form and fix the coating film and thus can beapplied to various kinds of metal materials such as irons, steels, zincalloys, aluminum alloys and magnesium alloys. It is however difficult toform and fix (bake, dry) the coating film onto complicate structuralparts e.g. vehicle parts uniformly by the surface modification techniqueof Patent Document 1. In particular, there is a problem in the surfacemodification technique of Patent Document 1 that the coating film doesnot have high durability and good adhesion to magnesium alloys.

It is accordingly an object of the present invention to provide amagnesium alloy member consisting of or comprising a magnesium alloymaterial formed with an active surface modified layer to achieve goodadhesion (bonding/coating) properties.

According to an aspect of the present invention, there is provided amagnesium alloy member, consisting of or comprising: analuminum-containing magnesium alloy material, the magnesium alloymaterial having a modified layer formed at a surface thereof in such amanner that at least a surface of the modified layer has a higheraluminum content than that of any unmodified base portion of themagnesium alloy material.

The other objects and features of the invention will also becomeunderstood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a magnesium alloy member according to oneembodiment of the present invention.

FIG. 2 is a schematic view of a magnesium alloy member according to amodification of the one embodiment of the present invention.

FIG. 3 is a schematic view of a magnesium alloy member according toanother modification of the one embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

The present invention will be described below with reference to thedrawings. In the following description, all percentages “%” are by massunless otherwise specified.

As shown in FIG. 1, a magnesium alloy member according to one embodimentof the present invention has a main body made of an aluminum-containingmagnesium alloy material 1, wherein the magnesium alloy material 1 has amodified layer 1 a formed at a surface thereof in such a manner that atleast a surface of the modified layer 1 a has a higher aluminum contentthan that of any other unmodified (original) base portion 1 b of themagnesium alloy material 1. It is herein noted that, although themodified layer 1 a and the unmodified base portion 1 b are illustratedas two separate layers in FIG. 1 for the sake of simplicity, there mayor may not be a clear interface between the modified layer 1 a and theunmodified base portion 1 b.

The content of magnesium (Mg) in the surface of the modified layer 1 arelatively decreases as the content of aluminum (Al) in the surface ofthe modified layer 1 a increases. This leads to a reduction in theamount of magnesium oxide, which is known to have poor adhesion to anadhesive or coating material, in the surface of the modified layer 1 aand facilitates the formation of a covalent bond or hydrogen bondbetween Al of the modified layer 1 a and a functional group of theadhesive or coating material. It is therefore possible to increase thesurface activity of the modified layer 1 a and improve the adhesion(bonding/coating) properties of the magnesium alloy material 1.

There is no particular restriction on the form of the magnesium alloymaterial 1. The magnesium alloy material 1 can be formed into any shapeby a known forming process such as mold casting, sand casting, diecasting, extrusion, forging and press forming.

There is also no particular restriction on the Al content of themagnesium alloy material 1 as long as the magnesium alloy material 1contains Al. It is preferable that the magnesium alloy material 1 has aninitial Al content of 2% or more (i.e. the Al content of the unmodifiedbase portion 1 b is 2% or more) in order to ensure the formation of theactive surface modified layer 1 a.

Specific examples of the magnesium alloy material 1 are those classifiedas AZ31, AZ31B, AZ61, AZ91, AZ91D, AM50, AM60 and AM60B according to SAE(Society of Automotive Engineers) J465. Herein, the alphabeticcharacters “AZ” and “AM” refer to the kinds of metal elements added inthe magnesium alloys where “A”, “M” and “Z” represent aluminum (Al),manganese (Mg) and zinc (Zn), respectively. The numerals after thealphabetic characters indicate the amounts of the metal elements added.For example, AZ91 alloy means that the alloy contains 9% aluminum and 1%zinc. Among others, AZ31, AZ61, AZ91, AM60 and AM60B alloys can betypically preferably used.

As other examples of the magnesium alloy material 1, there can be usedmagnesium alloy plates available under the trade names of AS21X(magnesium alloy plate containing 2% aluminum and 1% silicon) and MRI153(magnesium alloy plate containing 8% aluminum and 1% calcium).

The modified layer 1 a is not necessarily formed on the whole of thesurface of the magnesium alloy material 1 and may be formed on only arequired area of the surface of the magnesium alloy material 1 e.g. towhich an adhesive or coating material is to be applied.

In order to achieve particularly good adhesion (bonding/coating)properties, it is preferable that the Al content of the surface of themodified layer 1 a is made 1.5 times or more higher than that of theunmodified base portion 1 b.

There is no particular restriction on the process of formation of themodified layer 1 a (i.e. the process of surface modification of themagnesium alloy material 1). For example, the modified layer 1 a can beformed by surface treating the magnesium alloy material 1 withhigh-temperature steam. By such steam treatment, Mg element is elutedfrom the surface of the magnesium alloy material 1. This leads todisappearance of magnesium oxide from the surface of the magnesium alloymaterial 1 and migration and exposure of Al element from inside to thesurface of the magnesium alloy material 1. As a result, the Al contentof the surface and its vicinity of the magnesium alloy material 1becomes relatively increased to define the modified layer 1 a of higherAl content. The modified layer 1 a can alternatively be formed by anyother process such as aluminum plating or ion implantation.

It is preferable to form the modified layer 1 a by immersion treatmentof the magnesium alloy material 1 in an aqueous treatment solutioncontaining at least one kind of inorganic chloride.

Preferred examples of the inorganic chloride contained in the aqueoustreatment solution are metal chlorides such as lithium chloride,rubidium chloride, potassium chloride, barium chloride, strontiumchloride, calcium chloride, sodium chloride and magnesium chloride.These chlorides can be used solely or in combination of two or morethereof.

The inorganic chloride, notably metal chloride, has the feature ofsimply ionizing to a chloride ion and a metal ion (cation) and showshigh solubility in water. The hydroxy ion concentration of the aqueoustreatment solution thus increases with the addition of the inorganicchloride. The immersion treatment of the magnesium alloy material 1 insuch an aqueous chloride solution allows Mg element to be elutedpreferentially from the surface of the magnesium alloy material 1 andthereby allows Al element to be migrated and exposed to the surface ofthe magnesium alloy material 1 so that the Al content of the surface andits vicinity of the magnesium alloy material 1 becomes relativelyincreased. This makes it possible to form the modified layer 1 aefficiently with high reliability without causing deteriorations in thestrength of the magnesium alloy material 1 and in the durability of themodified layer 1 a. This is also effective in forming a double hydroxideat the surface of the modified layer 1 a as will be explained later.

The chlorine concentration of the aqueous treatment solution ispreferably in the range of 0.004 mol % to saturation concentration so asto prevent the inorganic chloride from being precipitated as an adhesioninhibition factor on the surface of the magnesium alloy material 1.

As one preferred example of the aqueous treatment solution, there can beused an aqueous lubricant (working fluid) that contains at least onekind of inorganic chloride and a surfactant. The aqueous lubricant isapplicable to any machining process such as grinding with a grindstoneor grinder, polishing with a sand paper, polishing cloth or polishingbelt and cutting with a drill, milling cutter, saw or any other cuttingtool.

The inorganic chloride is uniformly dispersed in the aqueous lubricantby the surfactant. The use of such an aqueous lubricant enables surfacemodification of the magnesium alloy material 1 by the uniformlydispersed inorganic chloride simultaneously with machining of themagnesium alloy material 1. This makes it possible to efficiently formthe uniform and stable modified layer 1 a and improve the adhesion(bonding/coating) properties of the magnesium alloy material 1 withoutcausing deteriorations in the strength of the magnesium alloy material 1and in the durability of the modified layer 1 a. This also contributesto improvement in the stability of ground treatment such as chemicalconversion treatment or primer coating treatment and reduction in theamount of mineral or synthetic oil residue after the machining.

There is no particular restriction on the inorganic chloride containedin the aqueous lubricant. Various kinds of inorganic chlorides such asammonium chloride can be used. The inorganic chloride is preferably ametal chloride. Preferred examples of the metal chloride contained inthe aqueous lubricant are those indicated above. These chlorides can beused solely or in combination of two or more thereof.

Further, the content of the inorganic chloride in the aqueous lubricantis preferably adjusted in such a manner that the chlorine concentrationof the aqueous lubricant is in the range of 0.004 mol % to saturationconcentration. When the chloride concentration of the aqueous lubricantis in the above range, the modified layer 1 a can be formed uniformlyand stably without the inorganic chloride being precipitated as anadhesion inhibition factor on the surface of the magnesium alloymaterial 1.

As the surfactant, there can be used anionic surfactants such as: fattyacid surfactants e.g. fatty acid sodium salts, fatty acid potassiumsalts and α-sulfofatty acid ester sodium salts; linear alkylbenzenesurfactants e.g. sodium linear alkylbenzene sulfonates; higher alcoholsurfactants e.g. sodium alkylsulfate esters and sodium alkyl ethersulfate esters; alpha-olefin surfactants e.g. sodium α-olefinsulfonates; and normal paraffin surfactants e.g. sodium alkylsulfonates.The content of the surfactant in the aqueous lubricant is preferablyadjusted to about 0.1 to 1.6%.

Preferably, the surfactant contains an alcohol fraction in order toincrease the compatibility of the inorganic chloride, water andmineral/synthetic oil in the aqueous lubricant and thereby form themodified layer 1 a uniformly and stably.

Examples of the alcohol contained in the surfactant are those ofmonohydric, dihydric and trihydric alcohols each having a carbon numberof 1 to 10, such as methanol, ethanol, isopropyl alcohol, ethyleneglycol and glycerin. Two or more kinds of alcohols may be used incombination. The presence of such a kind of alcohol in the surfactanteffectively improves the compatibility of the inorganic chloride, waterand mineral/synthetic oil in the aqueous lubricant and the fluidity ofthe aqueous lubricant. As the inorganic chloride, water andmineral/synthetic oil are dispersed more uniformly in the aqueouslubricant, the modified layer 1 a can be formed uniformly and stablywithout variations due to fluctuations in the inorganic chlorideconcentration and without inhibition by the mineral/synthetic oil.Further, the aqueous lubricant becomes less likely to remain on thesurface of the magnesium alloy material 1. The amounts of the inorganicchloride and mineral/synthetic oil remaining as residues on the surfaceof the magnesium alloy material 1 after the machining can be reduced asthe inorganic chloride and mineral/synthetic oil are vaporized togetherwith the alcohol. The content of the alcohol in the aqueous lubricant isnot particularly restricted and is preferably 3 to 50% by volume.

In the present invention, the formation of the modified layer 1 a (i.e.the Al content of the surface of the magnesium alloy material 1) can bereadily confirmed by e.g. X-ray photoelectron spectroscopy (XPS) and,more specifically, by determining the contents (atomic %) of the metal(e.g. Al) and oxygen atoms in the surface of the magnesium alloymaterial 1 and the bond energies between the metal and oxygen atoms inthe surface of the magnesium alloy material 1 from XPS measurementresults.

Preferably, the surface of the modified layer 1 a contains a doublehydroxide of Mg and Al. For example, the Mg—Al double hydroxide can beformed by the treatment of the magnesium alloy material 1 with theaqueous treatment solution (aqueous lubricant) as explained above. TheMg—Al double hydroxide can alternatively be formed as a precipitate bymixing a mixed aqueous solution of divalent and trivalent metal saltswith an alkaline solution. Specific examples of the Mg—Al doublehydroxide are those represented by Mg_(8-x)Al_(2x)CO₂.nH₂O where x is aninteger of 2 to 5 and n is an integer of 0 or greater. In the abovechemical formula, carbon (C) is derived from magnesium carbonategenerated by reaction of Mg with carbon dioxide of the air.

The double hydroxide has the feature of readily forming a covalent bondor hydrogen bond with a functional group (such as acrylic group, epoxygroup, isocyanate group or hydroxyl group) of the adhesive or coatingmaterial. Further, the double hydroxide has the function ofsignificantly improving the adhesion and durability of the adhesive orcoating material under the cohesive force of crystalline water oradsorbed water of the double hydroxide. The formation of such a doublehydroxide contributes to improvement in the adhesion (bonding/coating)properties of the magnesium alloy material 1.

The formation of the double hydroxide at the surface of the modifiedlayer 1 a can be confirmed by e.g. Fourier transform infraredspectroscopy (FT-IR).

As shown in FIG. 2, the magnesium alloy member may further includes alayer of adhesive resin material 2 applied to the modified layer 1 a ofthe magnesium alloy material 1 and an counterpart material 3 bonded bythe adhesive resin material 2 to the modified layer 1 a of the magnesiumalloy material 1.

There is no particular restriction on the form of the counterpartmaterial 3. The counterpart material 3 can be in the form of anystructural component or article shaped to fit with the magnesium alloymaterial 1.

There is also no particular restriction on the kind of the counterpartmaterial 3. Various kinds of materials can be used as the counterpartmaterial 3.

Examples of the counterpart material 3 are: resin materials such aspolyolefin resins e.g. polyethylene (PE) and polypropylene (PP),polystyrene (PS) resins, polyvinyl chloride (PVC) resins, polyesterresins, polyamide (PA) resins, polyamideimide (PAI) resins,acrylonitrile-butadiene-styrene (ABS) resins, polycarbonate (PC) resins,polyacetal (POM) resins, acrylic resins, urea resins, melamine resins,epoxy resins, phenol (PF) resins and polyphenylene sulfide (PPS) resins;metal materials such as steels, aluminum alloys, magnesium alloys,copper alloys and titanium alloys; fabric materials of carbon fibers,aramid fibers, glass fibers, natural fibers etc.; rubber materials suchas natural rubbers, styrene-butadiene rubbers (SBR),acrylonitrile-butadiene rubbers (NBR) and ethylene-propylene rubbers(EPDM); glass materials; and ceramic materials. Among others, preferredare resin materials and metal materials. It is conceivable to use themagnesium alloy material 1 as the counterpart material 3 and therebyproduce the magnesium alloy member as a composite of the magnesium alloymaterials 1. In this case, it is preferable that the modified layers 1 aof the magnesium alloy materials 1 face each other via the adhesiveresin material 2.

There is no particular restriction on the kind of the adhesive resinmaterial 2 as long as the adhesive resin material 2 is capable of beingapplied to at least an required area e.g. an end area 1 c (but typicallythe whole) of the surface of the modified layer 1 a of the magnesiumalloy body 1 and being cured after mating the surfaces of the magnesiumalloy material 1 and the counterpart material 3 together. Variousadhesive resins can be used as the adhesive resin material 2.

Examples of the adhesive resin material 2 are: (1) hot melt resins ofpolyolefin type (e.g. polyethylene (PE) type, ethylene-vinyl acetate(EVA) type etc.), synthetic rubber type (e.g. polybutadiene (SBS) type,polyisoprene (SIS) type etc.), polyamide type and polyester type; (2)epoxy resins; (3) urethane resins; (4) natural rubbers and syntheticrubbers such as styrene-butadiene rubber (SBR), acrylonitrile-butadienerubber (NBR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR),butyl rubber (IIR) and butadiene rubber (BR); (5) acrylic resins such asthose called “Second Generation Acrylic Adhesives (SGA)”; (6) urearesins; (7) melamine resins; (8) phenol resins; and (9) silicone resins(including modified silicones).

There is also no particular restriction on the process of application ofthe adhesive resin material 2 to the modified layer 1 a of the magnesiumalloy material 1. The adhesive resin material 2 can be directly appliedto the modified layer 1 a of the magnesium alloy material 1 with abrush, may be immersed into a cloth and then applied from the cloth tothe modified layer 1 a of the magnesium alloy material 1, or may beapplied to the modified layer 1 a of the magnesium alloy material 1 witha painting machine such as a spray, a blade coater, an air knife coater,a roll coater, a bar coater, a gravure coater, a flow coater, a curtaincoater or an application gun or by any other application process such asdipping.

In order to accelerate the curing of the adhesive resin material 2, heattreatment and/or humidification treatment can be performed as requiredafter applying the adhesive resin material 2 to the magnesium alloymaterial 1 and mating the magnesium alloy material 1 and the counterpartmaterial 3. It is particularly preferable, in the case of using theepoxy resin, urethane resin or silicone resin as the adhesive resinmaterial 2, to accelerate the curing of the adhesive resin material 2 bytreatment under the conditions of a temperature of 40 to 150° C. and anhumidity of 30 to 100% RH (relative humidity).

Preferably, the adhesive resin material 2 is at least one selected fromthe group consisting of acrylic resins, urethane resins, epoxy resinsand silicone resins in order to achieve good workability, quick curingproperties as well as sufficient adhesion durability.

There is no particular restriction on the kind of the acrylic resinused. Various kinds of acrylic resins such as thermoplastic acrylicresins, thermosetting acrylic resins and moisture-curable acrylic resinscan be used for the adhesive resin material 2.

Specific examples of the thermoplastic acrylic resins are polymers andcopolymers of acrylic esters such as methyl methacrylate and ethylacrylate or methacrylic esters, in each of which an alkyl group of theester moiety can be methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, tert-butyl, n-hexyl, lauryl or stearyl. In the case of themethacrylic ester copolymer, two or more kinds of ester moieties may beused.

Specific examples of the thermosetting acrylic resins are copolymers oftwo or more kinds of monomers, one of which is selected from the groupconsisting of monomers having cross-linking functional groups (e.g.carboxyl, hydroxyl, amino, methylol, epoxy etc.), such as acrylic acid,methacrylic acid, acrylamide, methacrylamide, N-methylol acrylamide,allyl glycidyl ether and glycidyl methacrylate; and the other isselected from the group consisting of styrene, acrylic esters andmethacrylic esters having no cross-linking functional groups.

Specific examples of the moisture-curable acrylic resins aremethylcyanoacrylate, ethylcyanoacrylate, propylcyanoacrylate andbutylcyanoacrylate.

Among the above acrylic resins, preferred are thermosetting acrylicresins and moisture-curable acrylic resins.

The acrylic resin may contain an additive(s) as required. Examples ofthe additive are: (1) antioxidants such as hindered amine, hydroquinone,hindered phenol and sulfur-containing compound; (2) UV absorbers such asbenzophenone, benzotriazole, salicylate and metal complex salt; (3)weather resistance stabilizers such as metallic soap, organic andinorganic heavy metal salts and organic tin compound; (4) plasticizerssuch as phthalate ester, phosphoric ester and fatty ester; (5) waxessuch as paraffin wax, polymer wax, beeswax, spermaceti wax,low-molecular-weight polyolefin; (6) organic and inorganic fillers suchas calcium carbonate, kaoline, talc, mica, bentonite, clay, carbonblack, glass balloon, acrylic resin powder, phenol resin powder, ceramicpowder, zeolite and titanium oxide; (7) organic and inorganic fiberssuch as glass fiber, aramid fiber, carbon fiber, acrylic fiber, nylonfiber, polyester fiber, alumina fiber and boron fiber; (8) antistaticagents; (9) antimicrobial agents; (10) dehydrators; (11) flameretardants; (12) solvents; (13) pigments; (14) perfumes; (15)accelerators. These additives can be used solely or in combination oftwo or more thereof.

There is no particular restriction on the kind of the urethane resinused as long as the urethane resin contains a compound having two ormore isocyanate groups in its molecule. Various kinds of urethane resinscan be used for the adhesive resin material 2.

Specific examples of the compound with two or more isocyanate groupsare: aromatic diisocyanates such as 2,4-tolylene diisocyanate (2,4-TDI),2,6-tolylene diisocyanate (2,6-TDI), 4,4′-diphenylmethane diisocyanate(4,4′-MDI), 2,4′-diphenylmethane diisocyanate (2,4′-MDI), 1,4-phenylenediisocyanate, xylylene diisocyanate (XDI), tetramethylxylidenediisocyanate (TMXDI), tolidine diisocyanate (TODI) and 1,5-naphthalenediisocyanate (NDI); aliphatic diisocyanates such as hexamethylenediisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysinediisocyanate and norbornane diisocyanate (NBDI); alicyclic diisocyanatessuch as transcyclohexane-1,4-diisocyanate, isophorone diisocyanate(IPDI), H6-XDI (hydrogenated XDI) and H12-MDI (hydrogenated MDI);carbodiimide-modified diisocyanates obtained by modifying the abovediisocyanates with carbodiimide; isocyanurate-modified diisocyanatesobtained by the above diisocyanates with isocyanurate. These compoundscan be used solely or in combination of two or more thereof.

Among the above urethane resins, preferred are 4,4′-MDI, 2,4′-MDI, HDI,XDI and prepolymers thereof.

The urethane resin may additionally contain a polyol compound asrequired. The polyol compound is not particularly restricted as long asit has two or more hydroxyl groups in the molecule. Specific examples ofthe polyol compound are: polyetherpolyols such as polyethylene glycol(PEG), polypropylene glycol (PPG) and polytetramethylene ether glycol(PTMG) and polyesterpolyols of condensed type and lactone type. Amongothers, preferred are polyetherpolyols.

The urethane resin may also contain a catalyst as required. The catalystis not particularly restricted as long as it is capable of controlling(increasing or decreasing) the curing rate of the urethane resin.Examples of the catalyst are: monoamines such as triethylamine (TEA) andN,N′-dimethylcyclohexylamine (DMEDA); diamines such asN,N,N′,N′-tetramethylethylene diamine (TMEDA) andN,N,N′,N′-tetramethylhexane-1,6-diamine (TMHMDA); triamines such asN,N,N′,N″,N″-pentamethyldipropylene triamine (PMDPTA) and tetramethylguanidine (TMG); cyclic amines such as triethylenediamine (TEDA),N,N′-dimethyl piperazine (DMP) and N-methyl morpholine (NMMO); andalcohol amines such as dimethylamino ethanol (DMEA) andN-methyl-N′-(2-hydroxyethyl)-piperazine (MHEP). Among others, preferredare triamines and cyclic amines.

The urethane resin may further contain an additive as required. Examplesof the additive usable in the urethane resin are the same as thoseusable in the acrylic resin as mentioned above. Two or more kinds ofadditives can be used in combination.

There is no particular restriction on the kind of the epoxy resin usedas long as the epoxy resin contains an epoxy compound having two or moreepoxy groups and a curing agent. Various kinds of epoxy resins can beused for the adhesive resin material 2.

Specific examples of the epoxy compound are bisphenol A type epoxyresins, bisphenol F type epoxy resins, bisphenol AD type epoxy resins,phenol novolac type epoxy resins, cresol novolac type epoxy resins,biphenyl type epoxy resins, glycidyl ester type epoxy resins, alicyclictype epoxy resins and heterocyclic type epoxy resins. Among others,preferred are epoxy resins of bisphenol A type and bisphenol F type.

Specific examples of the curing agent are: aliphatic amines such asethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine(TETA), tetraethylenepentamine (TEPA), isophoronediamine (IPDA) andN-aminoethylpiperazine (N-AEP); aliphatic aromatic amines such asm-xylenediamine (MXDA); aromatic amines such as metaphenylene diamine(MPDA), diaminodiphenylmethane (DDM) and diaminodiphenylsulfone (DDS);other amines such as dicyandiamide (DICY) and adipic dihydrazide (AADH);modified polyamines such as epoxy compound-added polyamines,Michael-added polyamines and Mannich-added polyamines; polyamide amines;and acid anhydrides such as phthalic anhydride (PA), tetrahydrophthalicanhydride (THPA), hexahydrophthalic anhydride (HHPA),methyltetrahydrophthalic anhydride (MeTHPA), methylhexahydrophthalicanhydride (MeHHPA), methylnadic anhydride (MNA), dodecylsuccinicanhydride (DDSA), pyromellitic dianhydride (PMDA),benzophenonetetracarboxylic dianhydride (BTDA), ethylene glycolbis(anhydro-trimellitate) (TMEG), trimellitic anhydride (TMA) andpolyazelaic polyanhydride (PAPA). Among others, preferred are aliphaticamines, other amines, modified polyamines and polyamide amines.

The epoxy resin may additionally contain a catalyst as required. Thecatalyst is not particularly restricted as long as it is capable ofcontrolling (increasing or decreasing) the curing rate of the epoxyresin. Specific examples of the catalyst are tertiary amines such as2-(dimethylaminomethyl)phenol (DMP-10),2,4,6-tris(dimethylaminomethyl)phenol (DMP30), triethanolamines,tetramethylguanidine, pyridine, picoline, piperidine, pyrrolidine and1,8-diazabiscyclo(5,4,0)undecen-1 (DBU). Among others, DMP-10 and DMP-30are preferred.

The epoxy resin may further contain an additive as required. Examples ofthe additive usable in the epoxy resin are the same as those usable inthe acrylic resin and in the urethane resin as mentioned above. Two ormore kinds of additives may be used in combination.

There is also no particular restriction on the kind of the siliconeresin used. Various kinds of silicone resins such as thermosettingsilicone resins and moisture-curable silicone resins can be used.

Specific examples of the thermosetting silicone resins are compositionseach containing a vinyl group-containing organopolysiloxane and a Si—Hgroup-containing organohydroxypolysiloxane as main components andprepared by using a platinum complex as a catalyst.

Specific examples of the moisture-curable silicone resins aredealcoholization type silicone resins, deoximation type silicone resins,deacetate type silicone resins, deamidation type silicone resins anddeacetone type silicone resins.

Among the above silicone resins, preferred are moisture-curable siliconeresins.

The silicone resin may further contain an additive as required. Examplesof the additive usable in the silicone resin are the same as thoseusable in the acrylic resin, in the urethane resin and in the epoxyresin as mentioned above. Two or more kinds of additives may be used incombination.

There is no particular restriction on the use of the adhesive resinmaterial 2 as long as the adhesive resin material 2 is applied to therequired area of the surface of the magnesium alloy material 1 and curedafter mating the magnesium alloy material 1 and the counterpart material3. In view of adhesion durability, it is preferable to prepare anadhesive resin solution by diluting the adhesive resin material 2 with asolvent, applying the adhesive resin solution to the modified layer 1 aof the magnesium alloy material 1, remove the solvent by vaporizationand drying, further apply the adhesive resin material 2 with e.g. anapplication gun, and then, curing or hardening the adhesive resinmaterial 2 after mating the magnesium alloy material 1 and thecounterpart material 3. The adhesive resin material 2 may also beapplied to the mating surface of the counterpart material 3 as requiredbefore mating the magnesium alloy material 1 and the counterpartmaterial 3.

As explained above, the Al content of the surface of the modified layer1 a becomes increased to reduce the content of difficult-to-adheremagnesium oxide and facilitate the formation of a covalent bond orhydrogen bond between Al of the modified layer 1 a and the functionalgroup (such as acrylic group, epoxy group, isocyanate group or hydroxylgroup) of the adhesive resin material 2. It is therefore possible tosecure good adhesion of the magnesium alloy material 1 to thecounterpart material 3 via the adhesive resin material 2 for a longtime. Especially when the double hydroxide is formed at the surface ofthe modified layer 1 a, the adhesion of the magnesium alloy material 1(modified layer 1 a) to the counterpart material 3 via the adhesiveresin material 2 can be further enhanced by the formation of a covalentbond or hydrogen bond between the double hydroxide and the functionalgroup of the adhesive resin material 2 and by the cohesive force ofcrystalline water or adsorbed water of the double hydroxide. It is thuspossible for the magnesium alloy material 1 (modified layer 1 a) tosecure particularly high adhesion durability as compared to those ofconventional chemical conversion treatment and blasting treatment.

As shown in FIG. 3, the magnesium alloy member may alternatively have acoating 4 of ink or paint (hereinafter referred to as “coating material4”) applied by e.g. printing to the surface of the modified layer 1 a ofthe magnesium alloy material 1. It is possible to achieve good adhesionof the magnesium alloy material 1 to the coating material 4 by thephysical and chemical effects of the modified layer 1 a based on thesame principals as those of the case of adhesive bonding between themagnesium alloy material 1 (modified layer 1 a) and the counterpartmaterial 3 by the adhesive resin material 2 as shown in FIG. 2.

There is no particular restriction on the kind of the coating material 4as long as the coating material 4 is capable of being applied to atleast a required area (typically the whole) of the surface of themodified layer 1 a of the magnesium alloy material 1 (typically, thewhole surface of the modified layer 1 a of the magnesium alloy material1) so as to show the basic function of the ink or paint. Various kindsof ink and paint can be used. Examples of the ink are offset inks,printing inks, gravure inks and building inks. Examples of the paint areplastic paints, metal paints, ceramic paints, leather paints, conductivepaints, insulating paints, UV curable paints and electron-beam curablepaints.

There is also no particular restriction on the process of application ofthe coating material 4 to the modified layer 1 a of the magnesium alloymaterial 1. The coating material 4 can be applied to the modified layer1 a of the magnesium alloy material 1 in the same manner as the adhesiveresin material 2.

The present invention will be described in more detail below withreference to the following examples. These examples are, however, merelyillustrative and are not intended to limit the present inventionthereto.

Example 1

(Sample Production)

Potassium chloride was dispensed and dissolved in water by a stirrer,thereby preparing an aqueous treatment solution with a potassiumchloride content of 3%. A plate of magnesium alloy AS21X (having an Alcontent of 2%, a Si content of 1% and a size of 25×50×3 mm) was keptimmersed in the prepared aqueous treatment solution for 1 minute. Afterthat, the treated surface of the magnesium alloy plate was washed withwater and dried in a heated oven at 200° C. for 2 hours. The resultingmagnesium alloy plate was used as a test sample of the magnesium alloymaterial 1. In this example, the immersion treatment time was setrelatively short to reduce the amount of Al exposed at the surface ofthe modified layer 1 a; and the heating/drying process was conductedafter the immersion treatment process to evaporate water ofcrystallization and thereby remove a double hydroxide from the surfaceof the modified layer 1 a.

(Evaluation Tests)

The test sample of the magnesium alloy material 1 was evaluated for thesurface condition (i.e. the ratio of the Al content of the surface ofthe modified layer 1 a to the Al content of the unmodified base portion1 b and the presence or absence of a double hydroxide at the surface ofthe modified layer 1 a), initial adhesion and durable adhesion. Theprocedures of the evaluation tests were as follows.

Surface Condition

The treated surface of the magnesium alloy plate was analyzed using anX-ray photoelectron spectroscope “JPS-920” (available from JEOL Ltd.) tomeasure the bond energies (bond states) of the respective metal atoms inthe treated surface of the magnesium alloy plate. The Al content (mol %)of the treated surface of the magnesium alloy plate was determined fromthe analytical measurement results as the Al content of the surface ofthe modified layer 1 a. On the other hand, a magnesium alloy plate AS21Xwithout immersion treatment was polished in one direction for 1 minutewith a sand paper No. 320 and subjected to air blowing for 5 to 10minutes to remove foreign matters from its surface. The untreatedpolished surface of the magnesium alloy plate was analyzed in the samemanner using the same X-ray photoelectron spectroscope as above. The Alcontent (mol %) of the untreated polished surface of the magnesium alloyplate was determined from the analytical measurement results as the Alcontent of the unmodified base portion 1 b. The Al content ratio wasthen calculated by dividing the Al content of the modified layer 1 a bythe Al content of the unmodified base portion 1 b.

The treated surface of the magnesium alloy plate was also analyzed byFourier transform infrared spectroscopy (FT-IR) to measure the IRabsorption peaks of the compounds in the treated surface of themagnesium alloy plate as well as the bond states of the respective metalatoms in the treated surface of the magnesium alloy plate. The presenceor absence of a double hydroxide at the surface of the modified layer 1a was judged based on these analytical measurement results.

Initial Adhesion

An adhesion test sample was produced as follows. A silicone adhesive“TB1217H” (available from ThreeBond Co., Ltd.) and an aluminum alloyplate “ADC12” (having a size of 25×125×3 mm) were prepared in additionto the treated magnesium alloy plate. The adhesive was applied to an endarea of 10 mm in width of the treated surface of the magnesium alloyplate, followed by bonding an end area of the surface of the aluminumalloy plate to the end area of the treated surface of the magnesiumalloy plate by the adhesive. The resulting plate assembly was left for168 hours at room temperature. Herein, the application amount of theadhesive was adjusted in such a manner that the thickness of theadhesive after the curing was 2 mm.

The adhesion test sample was subjected to tensile shear test using anautograph (“AG-I 20kN” available from Shimadzu Corporation) to measurethe shear strength of the test sample.

After the tensile shear test, the rate of a surface area of the adhesiontest sample in which cohesive failure of the adhesive occurred to thetotal surface area of the adhesive applied was determined by visualinspection as the cohesive failure rate of the test sample.

Durable Adhesion

The same adhesion test sample as above was prepared, left in an engineoil 5W-30 (SM Strong Save X) at a controlled temperature of 50° C. for168 hours and further left at room temperature for 24 hours. After that,the test sample was evaluated for the shear strength and cohesivefailure rate in the same manner as above.

It is herein noted that the cohesive failure is a structural fracture ofthe adhesive. In general, there occurs an interfacial failure (i.e. aseparation at the interface between the magnesium alloy plate and theadhesive), rather than a cohesive failure, in the sample when theadhesion strength between the magnesium alloy plate and the adhesive islow. Further, the sample shows a high cohesive failure rate but a lowshear strength if the cohesive failure occurs in the sample due toincomplete cure of the adhesive. It can be thus said that: the higherthe adhesion strength between the magnesium alloy plate and theadhesive, the higher the shear strength and cohesive failure rate: and,the smaller the difference between the initial adhesion and the durableadhesion, the higher the adhesion durability.

The evaluation test results of Example 1 are indicated in TABLE 1.

Example 2

A test sample of the magnesium alloy material 1 was produced in the samemanner as in Example 1, except that the immersion treatment time was setto 5 minutes to allow a greater amount of Al to be exposed at thesurface of the modified layer 1 a, and evaluated in the same manner asin Example 1. The evaluation results are indicated in TABLE 1.

Example 3

A test sample of the magnesium alloy material 1 was produced in the samemanner as in Example 2, except that no heating/drying process wasperformed after the immersion treatment process to allow a doublehydroxide to remain in the surface of the modified layer 1 a, andevaluated in the same manner as in Examples 1 and 2. The evaluationresults are indicated in TABLE 1.

Example 4

A test sample of the magnesium alloy material 1 was produced in the samemanner as in Example 3, except for using a plate of magnesium alloy“AZ31” (having an Al content of 3% and a Zn content of 1%) in place ofthe magnesium alloy plate “AS21X”, and evaluated in the same manner asin Examples 1 to 3. The evaluation results are indicated in TABLE 1.

Example 5

A test sample of the magnesium alloy material 1 was produced in the samemanner as in Example 3, except for using a plate of magnesium alloy“AZ91” (having an Al content of 9% and a Zn content of 1%) in place ofthe magnesium alloy plate “AS21X”, and evaluated in the same manner asin Examples 1 to 4. The evaluation results are indicated in TABLE 1.

Example 6

A test sample of the magnesium alloy material 1 was produced in the samemanner as in Example 3, except for using a plate of magnesium alloy“MRI153” (having an Al content of 8% and a Ca content of 1%) in place ofthe magnesium alloy plate “AS21X”, and evaluated in the same manner asin Examples 1 to 5. The evaluation results are indicated in TABLE 1.

Comparative Example 1

The same magnesium alloy plate “AS21X” as used in Examples 1 to 3 wasprepared as a substrate. A surface of the magnesium alloy plate waspolished in one direction for 1 minute with a sand paper No. 320 andsubjected to air blowing for 5 to 10 minutes. No surface modification(immersion treatment) was performed on the magnesium alloy plate. Theresulting untreated magnesium alloy plate was used as a comparativesample of magnesium alloy material. The comparative sample was evaluatedin the same manner as in Examples 1 to 6. The evaluation results areindicated in TABLE 1.

Comparative Example 2

A comparative sample of magnesium alloy material was produced in thesame manner as in Comparative Example 1, except for using a plate ofmagnesium alloy “AZ31” (having an Al content of 3% and a Zn content of1%) in place of the magnesium alloy plate “AS21X”, and evaluated in thesame manner as in Examples 1 to 6. The evaluation results are indicatedin TABLE 1.

Comparative Example 3

A comparative test sample of magnesium alloy material was produced inthe same manner as in Comparative Example 1, except for using a plate ofmagnesium alloy “AZ91” (having an Al content of 9% and a Zn content of1%) in place of the magnesium alloy plate “AS21X”, and evaluated in thesame manner as in Examples 1 to 6. The evaluation results are indicatedin TABLE 1.

Comparative Example 4

A comparative test sample of magnesium alloy material was produced inthe same manner as in Comparative Example 1, except for using a plate ofmagnesium alloy “MRI153” (having an Al content of 8% and a Ca content of1%) in place of the magnesium alloy plate “AS21X”, and evaluated in thesame manner as in Examples 1 to 6. The evaluation results are indicatedin TABLE 1.

Comparative Example 5

A comparative test sample of magnesium material was produced in the samemanner as in Comparative Example 1, except for using a plate of puremagnesium in place of the magnesium alloy plate “AS21X”, and evaluatedin the same manner as in Examples 1 to 6. The evaluation results areindicated in TABLE 1.

TABLE 1 Magnesium alloy material Modified layer Al content Al contentDouble Kind (%) ratio* hydroxide Example 1 AS21X 2 1.30 Not formedExample 2 AS21X 2 1.50 Not formed Example 3 AS21X 2 1.50 Formed Example4 AZ31 3 1.55 Formed Example 5 AZ91 9 1.67 Formed Example 6 MRI153 111.64 Formed Comparative AS21X 2 1 Formed Example 1 Comparative AZ31 3 1Not formed Example 2 Comparative AZ91 9 1 Not formed Example 3Comparative MRI153 11 1 Not formed Example 4 Comparative Pure Mg 0 — Notformed Example 5 Initial adhesion Durable adhesion Cohesive CohesiveShear strength failure rate Shear strength failure rate (MPa) (%) (MPa)(%) Example 1 1.30 65 1.20 50 Example 2 1.40 70 1.25 60 Example 3 1.8080 1.30 100 Example 4 1.90 80 1.35 100 Example 5 1.85 85 1.30 100Example 6 1.90 80 1.25 100 Comparative 0.02 0 0.02 0 Example 1Comparative 0.20 0 0.02 0 Example 2 Comparative 0.50 0 0.02 0 Example 3Comparative 0.60 0 0.02 0 Example 4 Comparative 0.02 0 0.02 0 Example 5*Al content ratio: aluminum content of surface of modified layer dividedby aluminum content of unmodified base portion

As shown in TABLE 1, each of the test samples of Examples 1 to 6 inwhich the Al content of the surface of the modified layer 1 a was higherthan that of the unmodified base portion 1 b had excellent adhesionproperties such as good initial adhesion and high adhesion durability.In particular, the test samples of Examples 3 to 6 in which the doublehydroxide was formed at the surface of the modified layer 1 a had moreexcellent adhesion properties (better initial adhesion and higheradhesion durability).

On the other hand, no modified layer was formed in each of the samplesof Comparative Examples 1 to 5. Even if Al was contained in the surfaceof the sample, the Al content of aluminum in the surface of the samplewas not higher than that of the other remaining portion of the sample inComparative Examples 1 to 5. The samples of Comparative Examples 1 to 5had poor adhesion properties.

It has been shown by the above evaluation results that it is possible toimprove the adhesion of the magnesium alloy material 1 by forming themodified layer 1 a at the surface of the magnesium alloy material 1 insuch a manner that at least the surface of the modified layer 1 a has ahigher Al content than that of the unmodified base portion 1 b.

Example 7

(Sample Production)

An aqueous cutting oil “NEOCOOL Bio-60” (available from Matsumura

Oil Research Corp.) was diluted by 30 times with water and mixed withcalcium chloride (available from Kanto Chemical Co., Inc.) by a stirrer,thereby preparing an aqueous lubricant with a calcium chloride contentof 3%. It is herein assumed that, as the cutting oil “NEOCOOL Bio-60”has a composition of 30 to 40% of a base oil and 30% or more of a fattyacid surfactant and was diluted by 30 times with water, the surfactantcontent of the prepared aqueous lubricant was about 1%. On the otherhand, a plate of magnesium alloy “AZ31” (having a size of 25×50×3 mm)was provided. A surface of the magnesium alloy plate was repeatedlypolished in one direction for 1 minute with a sand paper No. 320 whileapplying the aqueous lubricant to the surface of the magnesium alloyplate. The magnesium alloy plate was then left for 5 to 10 minutes.After that, the surface of the magnesium alloy plate was washed withwater. The resulting machined magnesium alloy plate was used as a testsample of the magnesium alloy material 1.

(Evaluation Tests)

The test sample of the magnesium alloy material 1 was evaluated for thesurface condition (i.e. the presence or absence of a double hydroxide atthe surface of the modified layer 1 a and the cleanliness of the surfaceof the modified layer 1 a), initial adhesion and durable adhesion. Theprocedures of the evaluation tests were as follows.

Surface Condition

The machined magnesium alloy plate was left cooled to room temperatureand analyzed by Fourier transform infrared spectroscopy (FT-IR) tomeasure the IR absorption peaks of the compounds in the machined surfaceof the magnesium alloy plate as well as the bond states of therespective metal atoms in the machined surface of the magnesium alloyplate. The presence or absence of a double hydroxide at the surface ofthe modified layer 1 a was judged based on these analytical measurementresults.

Further, the machined surface of the magnesium alloy plate was wipedwith a filter paper of known weight. The increase in weight of thefilter paper before and after the wiping was divided by an area of thewiped surface of the magnesium alloy plate. The cleanliness of themachined surface of the magnesium alloy plate was rated by the divisionresult as follows.

-   Very good: 0 to 0.09 g/m²-   Good: 0.1 to 0.19 g/m²-   Not good: 0.2 to 0.29 g/m²-   Bad: 0.3 g/m² or more

Initial Adhesion and Durable adhesion

An adhesion test sample was produced using the machined magnesium alloyplate and evaluated for the initial adhesion and adhesion durability inthe same manner as in Examples 1 to 6.

The evaluation test results of Example 7 are indicated in TABLE 2.

Example 8

An aqueous lubricant was prepared in the same manner as in Example 7,except for using sodium chloride (available from Kanto Chemical Co.,Inc.) in place of calcium chloride. A test sample of the magnesium alloymaterial 1 was produced in the same manner as in Example 7 using theprepared aqueous lubricant, and then, was evaluated in the same manneras in Example 7. The evaluation results are indicated in TABLE 2.

Example 9

A cutting oil “NEOCOOL Bio-60” was diluted by 30 times with water andmixed by a stirrer with calcium chloride (available from Kanto ChemicalCo., Inc.) and with ethanol (available from Kanto Chemical Co., Inc.),thereby preparing an aqueous lubricant with a calcium chloride of 3% andan ethanol content of 30 vol %. A test sample of the magnesium alloymaterial 1 was produced in the same manner as in Example 7 using theprepared aqueous lubricant, and then, was evaluated in the same manneras in Examples 7 and 8. The evaluation results are indicated in TABLE 2.

Example 10

An aqueous lubricant was prepared in the same manner as in Example 9,except for using sodium chloride and isopropyl alcohol in place ofcalcium chloride and ethanol, respectively. A test sample of themagnesium alloy material 1 was produced in the same manner as in Example7 using the prepared aqueous lubricant, and then, was evaluated in thesame manner as in Examples 7 to 9. The evaluation results are indicatedin TABLE 2.

Example 11

An aqueous lubricant was prepared in the same manner as in Example 9,except for using potassium chloride and ethylene glycol in place ofcalcium chloride and ethanol, respectively. A test sample of themagnesium alloy material 1 was produced in the same manner as in Example7 using the prepared aqueous lubricant, and then, was evaluated in thesame manner as in Examples 7 to 10. The evaluation results are indicatedin TABLE 2.

Example 12

An aqueous lubricant was prepared in the same manner as in Example 9,except for using glycerin in place of ethanol. A test sample of themagnesium alloy material 1 was produced in the same manner as in Example7 using the prepared aqueous lubricant, and then, was evaluated in thesame manner as in Examples 7 to 11. The evaluation results are indicatedin TABLE 2.

Comparative Example 6

A PAO (poly-alpha-olefin) synthetic oil “SUPER MULPUS DX46” (availablefrom Nippon Oil Corporation) was diluted by 30 times with water andmixed by a stirrer with sodium chloride, thereby preparing an aqueouslubricant with a sodium chloride content of 3%. A test sample ofmagnesium alloy material was produced in the same manner as in Example 7using the prepared aqueous lubricant, and then, was evaluated in thesame manner as in Examples 7 to 12. The evaluation results are indicatedin TABLE 2.

Comparative Example 7

An aqueous lubricant was prepared in the same manner as in ComparativeExample 6, except for using potassium chloride in place of sodiumchloride. A test sample of magnesium alloy member was produced in thesame manner as in Example 7 using the prepared aqueous lubricant, andthen, was evaluated in the same manner as in Examples 7 to 12. Theevaluation results are indicated in TABLE 2.

Comparative Example 8

A PAO synthetic oil “SUPER MULPUS DX46” was diluted by 30 times withwater and mixed with ethanol by a stirrer, thereby preparing an aqueouslubricant with an ethanol content of 30 vol %. A test sample ofmagnesium alloy material was produced in the same manner as in Example 7using the prepared aqueous lubricant, and then, was evaluated in thesame manner as in Examples 7 to 12. The evaluation results are indicatedin TABLE 2.

Comparative Example 9

An aqueous lubricant was prepared in the same manner as in ComparativeExample 8, except for using isopropyl alcohol in place of ethanol. Atest sample of magnesium alloy material was produced in the same manneras in Example 7 using the prepared aqueous lubricant, and then, wasevaluated in the same manner as in Examples 7 to 12. The evaluationresults are indicated in TABLE 2.

Comparative Example 10

An aqueous cutting oil “NEOCOOL Bio-60” was diluted by 30 times withwater and stirred by a stirrer. This diluted cutting oil was used as anaqueous lubricant. A test sample of magnesium alloy material wasproduced in the same manner as in Example 7 using the above aqueouslubricant, and then, was evaluated in the same manner as in Examples 7to 12. The evaluation results are indicated in TABLE 2.

Comparative Example 11

An aqueous cutting oil “NEOCOOL Bio-60” was diluted by 30 times withwater and mixed with ethanol by a stirrer, thereby preparing an aqueouslubricant with an ethanol content of 30 vol %. A test sample ofmagnesium alloy material was produced in the same manner as in Example 7using the prepared aqueous lubricant, and then, evaluated in the samemanner as in Examples 7 to 12. The evaluation results are indicated inTABLE 2.

Comparative Example 12

An aqueous cutting oil “NEOCOOL Bio-60” was diluted by 30 times withwater and mixed by a stirrer with trichloroethylene (as an organicchloride available from Kanto Chemical Co., Inc.), thereby preparing anaqueous lubricant with a trichloroethylene content of 3%. A test sampleof magnesium alloy material was produced in the same manner as inExample 7 using the prepared aqueous lubricant, and then, was evaluatedin the same manner as in Examples 7 to 12. The evaluation results areindicated in TABLE 2.

Comparative Example 13

An aqueous lubricant was prepared in the same manner as in ComparativeExample 12, except for using tetrachloroethylene (as an organic chlorideavailable from Kanto Chemical Co., Inc.) in place of trichloroethylene.A test sample of magnesium alloy material was produced in the samemanner as in Example 7 using the prepared aqueous lubricant, and then,was evaluated in the same manner as in Examples 7 to 12. The evaluationresults are indicated in TABLE 2.

Comparative Example 14

A test sample of magnesium alloy material was produced in the samemanner as in Example 7, except that the polishing process was conductedwith the use of no lubricant, and then, evaluated in the same manner asin Examples 7 to 12. The evaluation results are indicated in TABLE 2.

TABLE 2 Aqueous lubricant Inorganic chloride Alcohol Content SurfactantContent Kind (%) content (%) Kind* (vol %) Example 7 CaCl₂ 3 1 None —Example 8 NaCl 3 1 None — Example 9 CaCl₂ 3 1 EtOH 30 Example 10 NaCl 31 IPA 30 Example 11 KCl 3 1 EG 30 Example 12 CaCl₂ 3 1 GLY 30Comparative NaCl 3 — None — Example 6 Comparative KCl 3 — None — Example7 Comparative None — — EtOH 30 Example 8 Comparative None — — IPA 30Example 9 Comparative None — 1 None — Example 10 Comparative None — 1EtOH 30 Example 11 Comparative ClHC═CCl₂ 3 1 None — Example 12Comparative Cl₂C═CCl₂ 3 1 None — Example 13 Comparative None — — None —Example 14 Initial adhesion Durable adhesion Surface condition ShearCohesive Shear Cohesive Double Surface strength failure rate strengthfailure rate hydroxide cleanliness (MPa) (%) (MPa) (%) Example 7 FormedGood 1.5 65 0.9 75 Example 8 Formed Good 1.4 65 0.9 70 Example 9 FormedVery good 1.8 80 1.2 80 Example 10 Formed Very good 1.7 80 1.1 80Example 11 Formed Very good 1.8 85 1.3 90 Example 12 Formed Very good1.9 80 1.1 90 Comparative Not formed Bad 1.2 40 0.2 0 Example 6Comparative Not formed Bad 1.1 35 0.1 0 Example 7 Comparative Not formedGood 0.5 10 0.1 0 Example 8 Comparative Not formed Good 0.4 10 0.1 0Example 9 Comparative Not formed Not good 0.3 15 0.1 0 Example 10Comparative Not formed Good 0.5 15 0.1 0 Example 11 Comparative Notformed Bad 1.1 30 0.2 0 Example 12 Comparative Not formed Bad 1.0 40 0.10 Example 13 Comparative Not formed Bad 0.1 0 0.1 0 Example 14 *EtOH:ethanol, IPA: isopropyl alcohol, EG: ethylene glycol, GLY: glycerin

As shown in TABLE 2, the formation of the double hydroxide at thesurface of the modified layer 1 a was confirmed in each of the testsamples of Examples 7 to 12. Further, there was less residue of mineralor synthetic base oil remaining on the surface of the test sample; andthe surface of the test sample was generally clean in Examples 7 to 12.All of the test samples of Examples 7 to 12 had excellent adhesionproperties such as good initial adhesion and high adhesion durability.

On the other hand, no double-hydroxide-containing modified layer wasformed in each of the samples of Comparative Examples 6 to 14. Theresidue of mineral or synthetic base oil on the surface of the samplewas confirmed in each of Comparative Examples 6 to 14. The samples ofComparative Examples 6 to 14 had poor adhesion properties.

It has been shown by the above evaluation results that it is possible toform the surface modified layer 1 a containing the double hydroxide,without the mineral or synthetic oil residue remaining on the surface ofthe modified layer 1 a, and thereby possible to further improve theadhesion properties of the magnesium alloy material 1 by machining themagnesium alloy material 1 with the use of the aqueous lubricantcontaining at least one kind of inorganic chloride and surfactant.

The entire contents of Japanese Patent Application No. 2009-158432(filed on Jul. 3, 2009) and No. 2009-158431 (filed on Jul. 3, 2009) areherein incorporated by reference.

Although the present invention has been described with reference tospecific embodiments of the invention, the invention is not limited tothe above-described embodiments. Various modification and variation ofthe embodiments described above will occur to those skilled in the artin light of the above teaching. The scope of the invention is definedwith reference to the following claims.

1. A magnesium alloy member, consisting of or comprising: analuminum-containing magnesium alloy material, the magnesium alloymaterial having a modified layer formed at a surface thereof in such amanner that at least a surface of the modified layer has a higheraluminum content than that of any unmodified base portion of themagnesium alloy material.
 2. The magnesium alloy member according toclaim 1, wherein the aluminum content of the unmodified base portion is2 mass % or higher.
 3. The magnesium alloy member according to claim 1,wherein the aluminum content of the surface of the modified layer is 1.5times or more higher than that of the unmodified base portion.
 4. Themagnesium alloy member according to claim 1, wherein the surface of themodified layer contains a magnesium-aluminum double hydroxide.
 5. Themagnesium alloy member according to claim 1, further comprising: anadhesive resin material applied to at least part of the surface of themodified layer; and a counterpart material bonded by the adhesive resinmaterial to the surface of the modified layer.
 6. The magnesium alloymember according to claim 5, wherein the adhesive resin material is atleast one selected from the group consisting of acrylic resins, urethaneresins, epoxy resins and silicone resins.
 7. The magnesium alloy memberaccording to claim 1, further comprising a coating material applied tothe surface of the modified layer.
 8. The magnesium alloy memberaccording to claim 1, wherein the modified layer is formed by surfacetreatment of the magnesium alloy material with an aqueous solutioncontaining an inorganic chloride.
 9. The magnesium alloy memberaccording to claim 8, wherein the inorganic chloride is a metalchloride.
 10. The magnesium alloy member according to claim 8, whereinthe aqueous solution is an aqueous lubricant containing the inorganicchloride and a surfactant.
 11. The magnesium alloy member according toclaim 9, wherein the metal chloride is at least one selected from thegroup consisting of lithium chloride, rubidium chloride, potassiumchloride, barium chloride, strontium chloride, calcium chloride, sodiumchloride and magnesium chloride.
 12. The magnesium alloy memberaccording to claim 10, wherein the surfactant contains an alcohol. 13.The magnesium alloy member according to claim 12, wherein the alcohol isat least one selected from the group consisting of monohydric, dihydricand trihydric alcohols each having a carbon number of 1 to 10.